Rechargeable metal halide battery

ABSTRACT

A rechargeable metal halide battery, in which a salt of an electroplatable metal and a halogen selected from the class consisting of chlorine, bromine and iodine is electrolyzed from solution in a liquid medium during the charging cycle and reformed during the discharging cycle, the battery comprising at least one electrode comprising an electrically conductive corrodible element and a barrier layer along one side of the corrodible element, the barrier layer being substantially inert and impermeable to halogen in concentrations present in the battery, substantially impermeable to the liquid medium, and having a volume resistivity, Rho , such that Rho d is not greater than about 0.1 ohm-in.2, where d is the thickness of the barrier layer, the electrode having a total interface resistance, per square inch of electrolyte-contacting surface, not greater than about 0.05 ohms.

United States Patent Zito, Jr.

[ 1 Feb. 8, 1972 [54] RECHARGEABLE METAL HALIDE BATTERY [72] Inventor:Ralph Zito, .Ir., Westford, Mass.

[73] Assignee: The Zito Company, Inc., Derry, N.H.

[22] Filed: Oct. 20, 1969 211 Appl. No.: 867,799

s21 uslfl .136/6, 136/30 [58] l leldolsearch ..136/6,30,83,86, 154-155,136/121-122, 22, 100, 103

[56] References Cited UNITED STATES PATENTS 3,328,202 6/1967 Riffe..l36/30 x 3,382,102 5/l968 ZitO, Jr. ..136/30 3,320,093 5/1967 Harding61 al. ....136/122 3,285,781 11/1966 Zito, Jr. ....l36/6 x 3,408,23210/1968 Blue et al ..l36/30 2,853,444 9/1958 Pye et a]. ..204/l08Primary ExaminerAnthony Skapars Attorney-E. H. Kent ABSTRACT Arechargeable metal halide battery, in which a salt of an electroplatablemetal and a halogen selected from the class consisting of chlorine,bromine and iodine is electrolyzed from solutionin a liquid mediumduring the charging cycle and reformed during the discharging cycle, thebattery comprising at least one electrode comprising an electricallyconductive corrodible element and a barrier layer along one side of thecorrodible element, the barrier layer being substantially inert andimpermeable to halogen in concentrations present in the battery,substantially impermeable to the liquid medium, and having a volumeresistivity, p, such that pd is not greater than about 0.1 ohm-inf,where d is the thickness of the barrier layer, the electrode having atotal interface resistance, per square inch of electrolyte-contactingsurface, not greater than about 0.05 ohms.

30 Claims, 3 Drawing Figures RECl-IARGEABLE METAL IIALIDE BATTERY Thisinvention relates to secondary batteries and battery components.

One object of this invention is to provide inexpensive, rechargeable,reliable, high-capacity energy cells.

Another object is to provide improved batteries of simple, economicalconstruction having a high watt-hours/pound output, and reasonablecharge and discharge times.

Another object is to provide improved batteries which operate at ambienttemperatures and pressures, for running moderate power devices, such aslawn mowers and other garden tools, power tools, small electric vehicles(e.g., golf carts), and the like.

A further object is to provide a metal halide battery which is safe andreliable, has an energy output at least comparable to alkaline-typebatteries, and yet is lightweight, durable, and relativelymaintenance-free.

Still another object is to provide a safe, economical, and simple zincbromide battery.

The invention features a rechargeable metal halide battery, in which asalt of an electroplatable metal and a halogen selected from the classconsisting of chlorine,-bromine and iodine is electrolyzed from solutionin a liquid medium during the charging cycle and reformed during thedischarging cycle, the battery comprising at least one electrodecomprising an electrically conductive corrodible element and a barrierlayer along one side of the corrodible element, the barrier layer beingsubstantially inert and impermeable to halogen in concentrations presentin the battery, substantially impermeable to the liquid medium, andhaving a volume resistivity, p, such that pd is not greater than about0.1 ohm-in where d is the thickness of the barrier layer, the electrodehaving a total interface resistance, per square inch ofelectrolyte-contacting surface, not greater than about 0.05 ohms.

A preferred electrode has a barrier layer comprising highlyelectroconductive carbon particles (e.g., graphite and ,carbon black)and a bonding agent which is substantially inert and impermeable tohalogen in concentrations present in the battery adhered to a metalconductive element. For use as a cathode, the electrodepreferablyincludes additionally a halogen entrapment layer bonded to the barrierlayer which is inert to halogen in concentrations present in the batteryand comprises a halogen entrapping substance. For use as an anode, theelectrode has an electroplating surface provided by the barrier layer,and this surface is preferably rough so as to provide a large number ofelectroplating sites.

i In a preferred metal halide battery, two such electrodes are providedto function as end electrodes (e.g., as the sole electrodes in asingle-cell batt ry), one a cathode including a halogen entrapment layerand the other an anode having an electroplating surface on the barrierlayer, the end electrodes providing means for connecting the battery toexternal electrical equipment. If the battery is to be bipolar,composite electrodes may be located between the end electrodes. Eachcomposite electrode preferably includes an electrically conductingportion (e.g., of highly electroconductive carbon particles and ahalogen-inert bonding agent), having a resistivity, p, such that pd isnot greater than about 0.1 ohm-in where d is the thickness of theconducting portion, the conducting portion having an electroplatingsurface on one side, and a halogen entrapment portion bonded to theother side of the conducting 7 portion, the entrapment portion havingcharacteristics identical to those of the entrapment layer of the endcathode.

The end and composite electrodes are preferably constructed so that theprojected area of each cathode surface, projected across the batteryonto the adjacent electroplating anode surface, is less than thecross-sectional area of the electroplating surface. Thus, peripheralareas of the electroplating surface, which do not face any cathodesurface, will be effectively removed from the main electrical paththrough the battery. Metal deposition can then be confined to interiorportions of the electroplating surfaces, and plating along the edges ofthe anode substantially prevented. The effective cross-sectional area ofthe cathode may be defined, e.g., by ac tually constructing the cathodeto have such an area, by masking peripheral portions of the cathode withelectrical-insulating material, or by constructing the battery casing tohave structure projecting between the cathode and the anode. Preferably,a porous separator is placed between adjacent cathode and anode surfacesto lessen the tendency of halogen to migrate from the halogen-entrapmentlayer of the cathode to the anode.

Where the halogen is bromine (with which a preferred electroplatablemetal is zinc), a preferred entrapping substance is a bromine-adsorbent,such as activated carbon. A bonding agent for the barrier and entrapmentlayers of the end electrodes, useful with bromine, is a polymer bothinert and impermeable to bromine in concentrations present in thebattery and selected from the class consisting of polyfluorocarbons,polychlorofluorocarbons (e.g., polymonochlorotrifluoroethylene),polymers of monomers containing a major portion of vinylidene chloride,poly (vinyl chloride), and poly (methyl methacrylate). Since theentrapment layer bonding agent need not be bromine-impermeable, inasmuchas the barrier layer is bromine'inert, polyethylene and polypropylenemay be used. For the composite electrode, any of the above-describedbonding agents, including somewhat bromine-permeable bonding agents, maybe used. For each end or composite electrode, it is preferable, wherepossible (i.e., except when the entrapment layer bonding agent isbromine-permeable), that identical bonding agents be utilized in theentrapment and barrier layers, or the entrapment and conductingportions.

In another aspect, the invention features an electrode for an aqueouszinc bromide battery comprising an electrically conductive metallicelement and a barrier layer, along the metallic element, the barrierlayer consisting, by weight, of at least about 25 percent highlyelectroconductive carbon particles (e.g., graphite or carbon black) andthe remainder by weight of a polymeric bonding agent therefor, thebonding agent being substantially inert and impermeable to bromine inconcentrations present in the battery, and the barrier layer beingsubstantially impermeable to bromine and water. Where a cathode, theelectrode also includes a bromine-adsorbent layer, bonded to the barrierlayer, consisting, by weight, of a major portion of activated carbonparticles and a minor portion of a polymeric bonding agent therefor, thebonding agent being substantially inert to bromine in concentrationspresent in the battery; this adsorbent bromine layer permits the fiow ofelectricity between the electrolyte and barrier layer and has a bromineadsorptivity of at least about 0.5 grams of bromine per gram ofadsorbent layer. This electrode, whether anode or cathode, preferablyhas all portions of the metallic element masked both from bromine andelectrolyte by the barrier layer and, where required, by an additionalprotective film which is impermeable to either or both of bromine andthe electrolyte, and is formed of bromine-inert material.(e.g.,comprises one of the aforesaid polymeric bonding agents).

A preferred metallic element has apertures (e.g., is a screen) so thatit may be sandwiched between a barrier and a protective layer, which arebonded to each other through the apertures in the metal. For such aconstruction, it is preferred that an identical bonding agent be used inthe barrier layer and in the protective layer.

Other objects, features and advantages will appear to one skilled in theart from the following description of preferred embodiments of thepresent invention, taken together with the attached drawings thereof, inwhich:

FIG. 1 is a sectional view of a schematic illustration of a batteryembodying the present invention;

FIG. 2 is a sectional view, partially broken away, of the battery ofFIG. 1 along line 2-2 thereof; and,

FIG. 3 is another sectional view of the battery of FIG. 1, along line3-3 thereof.

The figures show a battery 10 having an outer case 12, an end (battery)cathode 14 electrically connected to cathode terminal screw 15, an end(battery) anode l8 electrically connected to anode terminal screw 20,one intermediate composite electrode 22, and a liquid electrolyte medium23.

Referring to FIG. 2, end cathode 14 includes a halogen-entrapment (e.g.,halogen-adsorbent) layer 24, having an extended surface 25 in contactwith electrolyte 23, and bonded, along its opposite surface, to barrierlayer 28, which is substantially impermeable both to halogen (byhalogen" is meant chlorine, bromine, and iodine, but not fluorine) andto electrolyte. Halogen-entrapment layer 24 is substantially inert tohalogen but preferably somewhat halogen-permeable. Metal screen 32 issandwiched between barrier layer 28 and a protective layer 34, the twolayers preferably being bonded to one another through the apertures inscreen 32. Protective layer 34 is substantially inert and impermeable tohalogen, as well as impermeable to electrolyte.

Barrier layer 28 should be capable of conducting electricity betweenentrapment layer 24 and metal screen 32, and thus should have aresistivity, p, and thickness, 11, such that pd is equal to or less thanabout 0.1 ohm-m Halogen-entrapment layer 24 preferably permits the flowof electricity between electrolyte and barrier layer, where relativelyfast battery charge and discharge times are desired. Exposed portions ofbarrier layer 28 and screen 32 may be coated with a protective film, 35,which is also substantially inert and impermeable to halide as well asimpermeable to electrolyte, and is an electrical insulator.

End anode 18 has a metal screen 38 sandwiched between an anode barrierlayer 40 and an anode protective layer 42, which have propertiesidentical, respectively, to cathode screen 32, barrier layer 28, andprotective layer 34. Anode barrier layer 40 has a roughened surface 44(e.g., sandblasted) in contact with the electrolyte providing a metalelectroplating surface. Exposed portions of screen 38 are coated with aprotective film 45, which is inert and impermeable to bromine and toelectrolyte.

Composite electrode 22 has a substantially halogen-inert conductingportion 46, including on one side a roughened electroplating surface 48(like electroplating surface 44 of anode 18) and, bonded. to itsopposite side, a halogen-entrapment (e.g., halogen-adsorbent) portion50, also substantially inert to halogen, and a protective electricalinsulator film 52, which may be identical to protective film 33.Halogen-entrapment portion 50 has an extended surface 53 in contact withelectrolyte 23. Conducting portion 46 should have a combinedresistivity, p, and thickness, d, such that pd is less than or equal toabout 0.1 ohm-inf. Entrapment portion 50 should permit flow ofelectricity between the electrolyte and conducting portion 50.

Porous separators 60, having spaced vertical ribs 62, are locatedbetween each adjacent anodic and cathodic surface, and retard thetendency of halogen molecules to migrate to the anode, thereby improvingthe charge retentivity of the battery. Since halogen-entrapment surfaces25, 53 are of smaller cross-sectional area that the adjacent anodic,electroplating surfaces 48, 44, respectively, very little metal will beelectroplated near the edges of the electroplating surfaces. Protectivefilms 35 and 52, made of electrical insulating material, further confinethe effective areas of the cathode. Case 12 may be constructed withhorizontally extending electrical insulating barriers 70, 72 which willeven further limit the effective cathode area.

In order to ensure an adequate battery output, the interface resistancefor each total cathode or anode electrolyte-contacting surface (whetherfor an end or for a composite electrode) should be, per square inch ofelectrolyte-contacting area, not greater than about 0.05 ohms. Thus, forcomposite electrode 22, the total interface resistance across theelectrode from electrolyte region 23a to electrolyte region 23b shouldnot be greater, per square inch of electrolyte contacting area, thanabout 0.10 ohms.

The electrolyte includes a liquid medium having a dissolved salt of ahalide and an electroplatable metal which is electrolyzed during thecharging cycle of the battery (i.e., by connecting a voltage sourceacross the battery to terminal screws 15 and 20), the metalelectroplating on the anode electroplating surfaces, and the halideforming a molecular halogen, which is substantially entrapped within thehalogen-entrapment layer or portion. The halogen-entrapping materialshould preferably form bonds with halogen molecules of sufficient energyto keep the halogen molecules near the cathode during charging andcharged periods, yet of low enough energy so as not to interfere withionization of halogen during the discharge cycle.

The halogen may be chlorine, bromine, or iodine. in general, the metalshould be repeatedly electroplatable and must not be corroded in theliquid electrolyte medium, and the metal halide salt must besufficiently soluble in the liquid medium to be electroplatable. Wherean aqueous liquid medium is employed, among the useful metals are, e.g.,zinc, nickel, cadmium, tin, lead, and copper. in a nonaqueouselectrolyte medium, such as may be utilized for chlorine, evenwater-unstable, reactive metals, such as sodium, potassium and lithiummay be used in addition to the above-listed metals, with suitablymetal-inert bonding agents.

A preferred electrolyte is zinc bromide in an aqueous solution. Thissalt has a reasonably high potential of 1.83 volts, is highly soluble inwater to provide a low resistivity electrolyte, and has a calculatedfree energy per pound of about 200 watthours. The molarity of theelectrolyte solution during charging and discharging is preferablybetween about 0.5 to 9, (more preferably, not more than about 7). Theelectrolyte is, of course, at its lowest molarity at full charge, andits highest at full discharge. Preferably, at full charge, substantiallyall free bromine in the battery is entrapped.

In the end cathode, for entrapping bromine, a preferred entrapment layerconsists of bromine-adsorbent activated carbon particles, bondedtogether by a bonding agent which is inert to bromine in concentrationspresent in the battery. Thus, bonding agents which might be degraded byconcentrated bromine (liquid), such as polymers having a major portionof vinylidene chloride, are nonetheless useable as an activated carbonbonding agent, so long as the concentrations of bromine produced in thebattery remainbelow those capable of degrading the bonding agent. ingeneral, when employing degradable polymers or copolymers of vinylidenechloride or vinyl chloride, the maximum bromine concentration in theadsorbent layer should not exceed about 0.5M. The bonding agent shouldpreferably merely bond the activated carbon particles together, withoutflowing into the adsorbent pores thereof, and should be present in theminimal amount required to give structural integrity to the adsorbentlayer. Preferably, the adsorbent layer adsorbs at least half its weightof bromine, and, more preferably an amount of bromine equal to or evengreater than its weight.

Among the sufficiently bromine-inert bonding agents suitable in theadsorbent layer are, e.g., the polyfluorocarbons, such aspolytetrafluoroethylene (Teflon, available from E. I. du Pont de Nemours& Co.), poly (vinylidene fluoride) Kynar, available from Penwalt Co.polymonochlorotrifluoroethylene (CTFE, available from Allied ChemicalCo.), and FEP," a fluorinated polyethylene available from the same duPont; poly (vinyl chloride) homopolymers (plasticized or unplasticized)(e.g., Geon 222, available from B. F. Goodrich Co.); poly (vinylidenechloride) homopolymers and copolymers (50 percent or greater vinylidenechloride) such as acrylonitrile and vinyl chloride copolymers (availablegenerally under the trade name Saran from Dow Chemical Co.);polymethacrylates such as poly (methyl methacrylates) (Plexiglas,"available from Rohm & Haas Co.); and polyalkylenes such as polyethyleneand polypropylene.

The adsorbent layer may be prepared by conventional methods, such as byadmixing the polymeric bonding agent and activated carbon particles in aliquid medium which is thereafter evaporated, or by sintering, or bymolding.

A preferred barrier layer, for use in a metal bromide battery, consistsof highly electroconductive carbon particles (e.g., graphite or carbonblack) bonded together by a bonding agent which is both inert andimpermeable to bromine, as well as impermeable to electrolyte, so as toprotect the metal connector (e.g., screen 32 or 38) beneath from thecorrosive effects of bromine, salt, and water, while allowing passage ofelectricity between the metal and the electrolyte. The metal substrateis typically copper or a similar highly conductive, yet corrodiblemetal.

The barrier layer bonding agent may, therefore, be any of the bondingagents previously listed for forming the adsorbent layer, except thepolyalkylenes which are somewhat too permeable to bromine. Wherebromine-degradable polymers, such as the vinyl chloride and vinylidenechloride polymers are employed, the maximum bromine concentration at thebarrier layer should not exceed about 0.5 M. Preferably, an identical orsimilar bonding agent is used in the adsorbent layer and in the barrierlayer, so that a good bond may be achieved between the layers. Where apolyalkylene is used in the adsorbent layer, a vinylidene chloridehomoor copolymer, e.g., may be utilized in the barrier layer. Theprotective layer, as well as the various protective films, for use in azinc bromide battery, may be constructed similarly to the barrier layer,or may consist simply of a film of any of the bonding agents utilized tobond the highly electroconductive carbon particles of the barrier layertogether. Preferably, to obtain a good bond through the metal screen,the bonding agent in the protective layer is identical to that in thebarrier layer. The protective layer should also be impermeable toelectrolyte.

The corrodible electrically conducting element is, e.g., a metal sheet,and enclosed in an envelope of bromine-inert and impermeable, andelectrolyte-impermeable material, such as a barrier layer and aprotective layer sealed to one another around the periphery of thesheet, and, in an end electrode, must have a portion connectable (e.g.,protruding from the battery) to an external electrical circuit.Preferably, the metal sheet has apertures (e.g., is a screen) so thatthe protective and barrier layers are bonded at spaced portions of themetal sheet.

For use in a metal bromide battery, a preferred end anode has a barrierlayer of highly electroconductive carbon particles (e.g., graphite orcarbon black) bonded together by one of the same group of bonding agentsutilized to make the end cathode barrier layer, and has a protectivelayer bonded through a metal sheet, such as a screen, to the barrierlayer, and formed in the same manner described for the cathodeprotective layer. The surface of the barrier layer which is in contactwith the electrolyte is roughened, e.g., by sandblasting, to form anirregular surface which thereby provides a great many sites for startingelectroplating of the metal, such as zinc. The metal also is therebyadhered better to the anodic surface, resulting in better chargeretentivity for the battery. in addition, uniform metal deposition isenhanced, lessening the possibility of excessive dendrite growth, aswell as ensuring a complete and reproducible discharge cycle for thebattery.

The entrapment portion of the composite electrode (or electrodes, thenumber depending on the voltage level desired for the battery) may,again, for a metal bromide battery, be composed of adsorbent activatedcarbon particles bonded together by a suitable substantiallybromine-inert bonding agent, such as listed above for the barrier layerof the end cathode. The conductive portion is composed of highlyelectroconductive carbon particles (e.g., graphite or carbon black)bonded together with one of the same group of bonding agents utilized inthe entrapment portion. Where, as shown in the illustrated embodiment,the composite electrode has no metal element, the somewhatbromine-permeable polyalkylenes are useful in the conductive portion,particularly where the required charge retention time is sufficientlylow (e.g., in the order of days) so that the rate of permeation ofsignificant bromine through to the electroplating surface of the anodeis so slow as to be negligible during the desired charge retention time.Where larger charge retention is desired (as when a "trickle" dischargebattery is desired), then less bromine-permeable materials such as thepolymeric fluorocarbons and chlorofluorocarbons, vinyl chlorides,vinylidene chlorides (homoand copolymers) and methacrylates arepreferred. Preferably, for good cohesion between the two portions of thecomposite electrode, the two bonding agents used in the two compositeelectrode portions are identical.

The separator 60 must have sufficient porosity to allow free passagetherethrough of electrolyte, yet not be so porous as to present noobstacle to free passage therethrough of bromine molecules. The poresmay be of substantially'larger size than bromine molecules, and stillpresent some impedance to, although not prevent entirely, passage ofbromine molecules. One useful separator material is a porous (pores inthe range of 200 to 500 Angstroms in diameter) polyethylene separator,structured as shown in the figures, having a thickness of about 1/32inch. Dialysis membranes (e.g., having pore sizes in the order of 50Angstroms) are also useful.

Iodine being less reactive than bromine, all of the bonding agentslisted for bromine are sufficiently inert to iodine for use as bondingagents in forming barrier and entrapment layers for metal iodinebatteries, whereas at least the polyfluorocarbons andpolychlorofluorocarbons are suitable bonding agents for metal chloridebatteries.

A preferred material for making the battery case is 3/16 inch poly(methyl methacrylate). The frame may be cemented to the cathodes using apolymeric material similar so that used for making the electrodes. Forexample, a Saran cement (e.g., a mixture of Saranl 30 resin, poly(methyl methacrylate) and a suitable solvent) is particularly useful forSaran or Plexiglas electrodes.

An illustrative method for preparing a battery in accordance with thepresent invention will now be described, utilizing poly(monochlorotrifluoroethylene). This method is generally applicable toother bonding agents, with the relative amounts of materials and moldingtemperatures suitably adjusted to provide electrodes having both therequired resistivities and adsorptivities, as well as mechanicalintegrity.

To prepare a barrier sheet useful as a barrier layer, 70 grams of CTFE,a commercially available polyrnonochlorotrifluoroethylene (availablefrom Allied Chemical Co.) was mixed in a blender for 10 minutes with 30grams of highly electroconductive graphite particles (Dixon No. l l 12).The mixture was introduced into a 6 X 9 inches X /s inch frame, andtrowelled until level. The frame was placed in a mold formed of twoplatens, heated for 1 minute at 530 F., and clamped between the platensunder 30 tons of pressure for 5 minutes. The pressure was then released,and the frame cooled between cold platens under 30 tons of pressure (forapproximately 5 minutes); the resultant (about 20 mils thick) sheet hada pd of less than 0.1 ohm-inf.

A copper substrate was prepared from a 5 mil copper sheet, 3 and )2inches by 8 inches, having 40 and one-eighth inch holes therethrough,both surfaces sandblasted, and the entire sheet cleaned in a 0.lNsolution of hexionic acid. If a copper screen is used, it should also becleaned in hexionic acid, and preferably prestraightened in a moldbetween cold 'platens at a pressure of 30 tons.

Two CTFE barrier sheets, prepared as described, were cut so as toprovide an approximately one-half inch border around the entireperiphery of the copper sheet, and these two CTFE sheets, with thecopper sheet placed therebetween and totally encased within the CTFEsheets, were placed in the mold, heated for one minute at 530 F., heldfor 5 minutes under 30 tons, and cooled in the mold for 5 minutes under30 tons. The resultant sheet, with the copper encased between thelaminated CTFE sheets, was left in the mold, and there was trowelledonto this sheet 26.5 grams of a mixture, ball milled for 14 minutes, ofpercent by weight activated carbon (Barneby Cheney UU grade) and 10percent by weight of CTFE. The mixturewas heated at 490 F. in the moldfor 2 minutes, pressed under tons pressure for minutes, and then cooledin the mold with the pressure maintained.

An anode was prepared by laminating a copper sheet between twographite-loaded CTFE barrier sheets, made as described, and thereaftersandblasting one surface of the resultant anode.

A composite electrode was prepared by producing a graphite-loaded CTFEbarrier sheet, made as described, in the mold, adding 26.5 grams of theabove-described mixture of activated charcoal and CTFE onto the sheet,and pressing the mixture together between hot platens as described formaking the cathode.

A single cell battery was constructed, utilizing the above describedCTFE end cathode and end anode, separated by a single porouspolyethylene separator. The total surface resistance across any one ofthe two electrolyte-contacting surfaces was, per square inch, with a 3.5(full discharge) molar solution of zinc bromide in water as anelectrolyte, not greater than about 0.05 ohms. The single-cell batterywas cycled more than 100 times, and had a total capacity of about 6 to 8watthours (about to 27 watt-hours/lb).

Other embodiments will occur to those skilled in the art.

What is claimed is:

l. A rechargeable metal halide battery, in which a salt of anelectroplatable metal and a halogen selected from the group consistingof chlorine, bromine, and iodine, is electrolyzed from solution in aliquid electrolyte medium during the charging cycle and reformed duringthe discharging cycle, comprising an electrode suitable for connectionto an external electrical circuit to charge and discharge said batterycomprising an electrically conductive element, corrodible by saidhalogen, for connection to said circuit, and

a separate barrier layer, for conducting current between said corrodibleelement and said liquid electrolyte medium, said barrier layer beingsecured along one side of said corrodible element to separate saidelement from said liquid electrolyte medium, said barrier layer beinginert and impermeable to said halogen in concentrations present in saidbattery, impermeable to said liquid medium, and having a volumeresistivity, p, such that pd is not greater than about 0.1 ohm-inF,where d is the thickness of the barrier layer,

said electrode having a total interface resistance, per square inch ofelectrolyte-contacting surface area, not greater than about 0.05 ohms.

2. A battery according to claim 1 wherein said barrier layer compriseshighly electroconductive carbon particles and a bonding agent inert andimpermeable to halogen in concentrations present in said battery.

3. A battery according to claim 2 wherein said halogen is bromine, andsaid bonding agent is a polymer inert and impermeable to bromine inconcentrations present in said battery, selected from the classconsisting of polyfluorocarbons, polychlorofluorocarbons, polymers ofmonomers containing a major portion of vinylidene chloride, poly (vinylchloride), and poly (methyl methacrylate).

4. A battery according to claim 3 wherein said polymer ispolymonochlorotrifluoroethylene.

5. A battery according to claim 1 wherein said electrode is a cathodeand comprises a halogen entrapment layer, inert to halogen inconcentrations present in said battery and comprising a halogenentrapping substance.

6. A battery according to claim 5 wherein said halogen is bromine andsaid halide entrapment layer comprises bromine absorbent particles and abonding agent for securing said particles into an integral layer, saidbonding agent being inert to bromine in concentrations present in saidbattery, said layer having a bromine adsorptivity of at least about 0.5g. of bromine per gram of said layer.

7. A battery according to claim 6 wherein said bonding agent is apolymer inert and impermeable to bromine, selected from the classconsisting of polyfluorocarbons, polychlorofluorocarbons, polymers ofmonomers containing a major portion of vinylidene chloride, poly (vinylchloride), poly (methyl methacrylate), polyethylene, and polypropylene.

8. A battery according to claim 7 wherein said polymer ispolymonochlorotrifluoroethylene.

9. A battery according to claim 6 wherein said bromine ad sorbent isactivated carbon.

10. A battery according to claim 1 wherein said electrode is an anode,and said barrier layer provides an electroplating surface for saidmetal.

11. A battery according to claim 10 wherein said electroplatable metalis zinc and said electroplating surface has a rough texture providing alarge number of electroplating sites for said metal.

12. A battery according to claim 1 wherein said electrically conductivecorrodible element is formed of metal.

13. A battery according to claim 1 comprising cathodic and anodicelectrodes including at least two said electrodes having said corrodibleelectrically conductive element and said barrier layer wherein one saidelectrode is a cathode comprising additionally a halogen entrapmentlayer, inert to halogen in concentrations present in said battery,bonded to said barrier layer, and comprising a halogen-entrappingsubstance, and

the other said electrode is an anode,

each cathodic electrode having an extended surface adapted to be locatedadjacent said liquid electrolyte medium,

and each said anodic electrode having an electroplating surface for saidmetal, parallel to the adjacent extended cathode surface.

14. A battery according to claim 13 wherein the projectedcross-sectional area of each extended cathode surface, projected acrosssaid battery onto the adjacent electroplating surface, is less than thecross-sectional area of said electroplating surface.

15. A battery according to claim 14 wherein the actual cross-sectionalarea of each extended cathode surface is less than the cross-sectionalarea of the adjacent electroplating surface.

16. A battery according to claim 14 including structure projectingbetween an extended cathode surface and an adjacent anode electroplatingsurface such that the projected cross-sectional area of the saidextended cathode surface across said battery onto said adjacentelectroplating surface is less than the actual cross-sectional area ofthe said extended cathode surface.

17. A battery according to claim 14 including a layer ofelectrical-insulating material along peripheral portions of an extendedcathode surface to limit said extended surface to said projectedcross-sectional area.

18. A battery according to claim 13 including a porous separator elementbetween adjacent cathode and anode surfaces, whereby the tendency ofhalogen to migrate from said cathode to said anode is lessened.

19. A battery according to claim 13 wherein said battery includes atleast one composite electrode intermediate of said anode and saidcathode, said composite electrode comprising an electrically conductiveportion inert to halogen in concentrations present in said battery,having a resistivity, p, such that pd is not greater than about 0.1ohm-inf, where d is the thickness of said element, and having a surface,facing said end cathode, providing an electroplating surface for saidmetal, and

a halogen entrapment portion, bonded to said electrically conductiveportion along the surface of said electrically conductive portionopposite said electroplating surface, said entrapment portion beinginert to halogen in concentrations present in said battery, comprising ahalogen-entrapping substance, and providing an extended surface facingsaid end anode,

said composite electrode having a total interface resistance,

per square inch of electrolyte-contacting surface areas, not greaterthan about 0.10 ohms.

20. A battery according to claim 19 wherein said composite electrodeelectroplating surface has a rough texture providing a large number ofelectroplating sites for said metal.

21. A battery according to claim 19 wherein said halogen is bromine.

22. A battery according to claim 21 wherein the said electricallyconductive portion of said electrode comprises highly electroconductivecarbon particles and a bonding agent inert to bromine in concentrationspresent in said battery, and said halogen-entrapment portion comprisesbromine-adsorbent activated carbon particles and a bonding agent forsecuring said particles into an integral layer, said bonding agent beinginert to bromine in concentrations present in said battery, saidhalogen-entrapment portion having a bromine adsorptivity of at leastabout 0.5 g. of bromine per gram of said portion.

23. A battery according to claim 21 wherein each said bonding agent is apolymer, to bromine in concentrations present in said battery, selectedfrom the class consisting of polyfluorocarbons, polychlorofluorocarbons,polymers of monomers containing a major portion of vinylidene chloride,poly (vinyl chloride), poly (methyl methacrylate), polyethylene, andpolypropylene.

24. A battery according to claim 23 wherein said electrode bondingagents are identical.

25. A battery according to claim 24 wherein said bonding agent ispolymonochlorotrifluoroethylene.

26. In a rechargeable metal bromide battery, in which a salt of anelectroplatable metal and a halogen selected from the group consistingof chlorine, bromine, and iodine is electrolyzed from solution in aliquid medium during the charging cycle and reformed during thedischarging cycle, said battery including an end anode and an endcathode structured to provide external electrical connections for saidbattery,

a composite electrode adapted to be located intermediate of said endanode and said end cathode in voltaic series therewith, said compositeelectrode comprising an electrically conductive portion comprisinghighly electroconductive carbon particles and a polymeric bonding agentbonding said particles together, said bonding agent being inert to saidhalogen in concentrations present in said battery, said conductiveportion having a resistivity, p, such that pd is not greater than about0.] ohm-in, where d is the thickness of said element, and having a surface, facing said end cathode, providing an electroplating surface forsaid metal, and

a separate bromine-adsorbent portion, bonded to said electricallyconductive portion along the surface of said electrically conductiveportion opposite said electroplating surface, comprisingbromine-adsorbent activated carbon particles and a polymeric bondingagent for securing said particles into an integral electrode portion,said bonding agent inert to bromine in concentrations present in saidbattery, having a bromine adsorptivity of at least about 0.5 g. ofbromine per g. of said portion, and providing an extended surface facingsaid end anode,

the bonding agent of said conducting portion and the bonding agent ofsaid adsorbent portion being adherent to one another to bond saidportions together,

said composite electrode having a total interface resistance,

per square inch of electrolyte-contacting surface area, not greater thanabout 0. 10 ohms.

27. A battery according to claim 26 wherein said composite electrodeelectroplating surface has a rough texture providing a large number ofelectroplating sites for said metal.

28. A battery according to claim 26 wherein each said bonding agent is apolymer, inert to bromine in concentrations present in said battery,selected from the class consisting of polyfluorocarbons,polychlorofluorocarbons, polymers of monomers containing a major portionof vinylidene chloride, poly (vinyl chloride), poly (methylmethacrylate), polyethylene, and polypropylene.

29. A battery according to claim 28 wherein said electrode bondin agentsare identical.

30. 1% battery according to claim 29 wherein said bonding agent ispolymonochlorotrifluoroethylene.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.3,6HO,77O Dated February 8, 1972 Inventor(s) Ralph ZILCO JI'.

It is certified that error appears in the above-identified patent andthat said Letters Patent are hereby corrected as shown below:

Col. 3, line 56, change "that" to --than--.

Col. 6, line 30, change "so" to ----to.

C01. 9, line 17, before "to" insert -inert.

Signed and sealed this 12th day of September 1972.

(SEAL) Attest;

EDWARD M.FLETCHER,JR. V ROBERT GOTTSCHALK Attesting Officer Commissionerof Patents FORM PO 1050 (10 69, USCOMIWDC 6o376 p69 u.sv GOVERNMENIPRINTING OFFICE: lss O-366334

2. A battery according to claim 1 wherein said barrier layer compriseshighly electroconductive carbon particles and a bonding agent inert andimpermeable to halogen in concentrations present in said battery.
 3. Abattery according to claim 2 wherein said halogen is bromine, and saidbonding agent is a polymer inert and impermeable to bromine inconcentrations present in said battery, selected from the classconsisting of polyfluorocarbons, polychlorofluorocarbons, polymers ofmonomers containing a major portion of vinylidene chloride, poly (vinylchloride), and poly (methyl methacrylate).
 4. A battery according toclaim 3 wherein said polymer is polymonochlorotrifluoroethylene.
 5. Abattery according to claim 1 wherein said electrode is a cathode andcomprises a halogen entrapment layer, inert to halogen in concentrationspresent in said battery and comprising a halogen entrapping substance.6. A battery according to claim 5 wherein said halogen is bromine andsaid halide entrapment layer comprises bromine absorbent particles and abonding agent for securing said particles into an integral layer, saidbonding agent being inert to bromine in concentrations present in saidbattery, said layer having a bromine adsorptivity of at least about 0.5g. of bromine per gram of said layer.
 7. A battery according to claim 6wherein said bonding agent is a polymer inert and impermeable tobromine, selected from the class consisting of polyfluorocarbons,polychlorofluorocarbons, polymers of monomers containing a major portionof vinylidene chloride, poly (vinyl chloride), poly (methylmethacrylate), polyethylene, and polypropylene.
 8. A battery accordingto claim 7 wherein said polymer is polymonochlorotrifluoroethylene.
 9. Abattery according to claim 6 wherein said bromine adsorbent is activatedcarbon.
 10. A battery according to claim 1 wherein said electrode is ananode, and said barrier layer provides an electroplating surface forsaid metal.
 11. A battery according to claim 10 wHerein saidelectroplatable metal is zinc and said electroplating surface has arough texture providing a large number of electroplating sites for saidmetal.
 12. A battery according to claim 1 wherein said electricallyconductive corrodible element is formed of metal.
 13. A batteryaccording to claim 1 comprising cathodic and anodic electrodes includingat least two said electrodes having said corrodible electricallyconductive element and said barrier layer wherein one said electrode isa cathode comprising additionally a halogen entrapment layer, inert tohalogen in concentrations present in said battery, bonded to saidbarrier layer, and comprising a halogen-entrapping substance, and theother said electrode is an anode, each cathodic electrode having anextended surface adapted to be located adjacent said liquid electrolytemedium, and each said anodic electrode having an electroplating surfacefor said metal, parallel to the adjacent extended cathode surface.
 14. Abattery according to claim 13 wherein the projected cross-sectional areaof each extended cathode surface, projected across said battery onto theadjacent electroplating surface, is less than the cross-sectional areaof said electroplating surface.
 15. A battery according to claim 14wherein the actual cross-sectional area of each extended cathode surfaceis less than the cross-sectional area of the adjacent electroplatingsurface.
 16. A battery according to claim 14 including structureprojecting between an extended cathode surface and an adjacent anodeelectroplating surface such that the projected cross-sectional area ofthe said extended cathode surface across said battery onto said adjacentelectroplating surface is less than the actual cross-sectional area ofthe said extended cathode surface.
 17. A battery according to claim 14including a layer of electrical-insulating material along peripheralportions of an extended cathode surface to limit said extended surfaceto said projected cross-sectional area.
 18. A battery according to claim13 including a porous separator element between adjacent cathode andanode surfaces, whereby the tendency of halogen to migrate from saidcathode to said anode is lessened.
 19. A battery according to claim 13wherein said battery includes at least one composite electrodeintermediate of said anode and said cathode, said composite electrodecomprising an electrically conductive portion inert to halogen inconcentrations present in said battery, having a resistivity, Rho , suchthat Rho d is not greater than about 0.1 ohm-in.2, where d is thethickness of said element, and having a surface, facing said endcathode, providing an electroplating surface for said metal, and ahalogen entrapment portion, bonded to said electrically conductiveportion along the surface of said electrically conductive portionopposite said electroplating surface, said entrapment portion beinginert to halogen in concentrations present in said battery, comprising ahalogen-entrapping substance, and providing an extended surface facingsaid end anode, said composite electrode having a total interfaceresistance, per square inch of electrolyte-contacting surface areas, notgreater than about 0.10 ohms.
 20. A battery according to claim 19wherein said composite electrode electroplating surface has a roughtexture providing a large number of electroplating sites for said metal.21. A battery according to claim 19 wherein said halogen is bromine. 22.A battery according to claim 21 wherein the said electrically conductiveportion of said electrode comprises highly electroconductive carbonparticles and a bonding agent inert to bromine in concentrations presentin said battery, and said halogen-entrapment portion comprisesbromine-adsorbent activated carbon particles and a bonding agent forsecuring said particles into an integral layer, said bonding agent beinginert to bromine in concentrations present in said battery, saidhalogen-entrapment portion having a bromine adsorptivity of at leastabout 0.5 g. of bromine per gram of said portion.
 23. A batteryaccording to claim 21 wherein each said bonding agent is a polymer,inert to bromine in concentrations present in said battery, selectedfrom the class consisting of polyfluorocarbons, polychlorofluorocarbons,polymers of monomers containing a major portion of vinylidene chloride,poly (vinyl chloride), poly (methyl methacrylate), polyethylene, andpolypropylene.
 24. A battery according to claim 23 wherein saidelectrode bonding agents are identical.
 25. A battery according to claim24 wherein said bonding agent is polymonochlorotrifluoroethylene.
 26. Ina rechargeable metal bromide battery, in which a salt of anelectroplatable metal and a halogen selected from the group consistingof chlorine, bromine, and iodine is electrolyzed from solution in aliquid medium during the charging cycle and reformed during thedischarging cycle, said battery including an end anode and an endcathode structured to provide external electrical connections for saidbattery, a composite electrode adapted to be located intermediate ofsaid end anode and said end cathode in voltaic series therewith, saidcomposite electrode comprising an electrically conductive portioncomprising highly electroconductive carbon particles and a polymericbonding agent bonding said particles together, said bonding agent beinginert to said halogen in concentrations present in said battery, saidconductive portion having a resistivity, Rho , such that Rho d is notgreater than about 0.1 ohm-in.2, where d is the thickness of saidelement, and having a surface, facing said end cathode, providing anelectroplating surface for said metal, and a separate bromine-adsorbentportion, bonded to said electrically conductive portion along thesurface of said electrically conductive portion opposite saidelectroplating surface, comprising bromine-adsorbent activated carbonparticles and a polymeric bonding agent for securing said particles intoan integral electrode portion, said bonding agent inert to bromine inconcentrations present in said battery, having a bromine adsorptivity ofat least about 0.5 g. of bromine per g. of said portion, and providingan extended surface facing said end anode, the bonding agent of saidconducting portion and the bonding agent of said adsorbent portion beingadherent to one another to bond said portions together, said compositeelectrode having a total interface resistance, per square inch ofelectrolyte-contacting surface area, not greater than about 0.10 ohms.27. A battery according to claim 26 wherein said composite electrodeelectroplating surface has a rough texture providing a large number ofelectroplating sites for said metal.
 28. A battery according to claim 26wherein each said bonding agent is a polymer, inert to bromine inconcentrations present in said battery, selected from the classconsisting of polyfluorocarbons, polychlorofluorocarbons, polymers ofmonomers containing a major portion of vinylidene chloride, poly (vinylchloride), poly (methyl methacrylate), polyethylene, and polypropylene.29. A battery according to claim 28 wherein said electrode bondingagents are identical.
 30. A battery according to claim 29 wherein saidbonding agent is polymonochlorotrifluoroethylene.